docs: def check_for_eni_source():
      ''' Juju removes the source line when setting up interfaces,
      replace if missing '''
  
      with open('/etc/network/interfaces', 'r') as eni:
          for line in eni:
              if line == 'source /etc/network/interfaces.d/*':
                  return
      with open('/etc/network/interfaces', 'a') as eni:
          eni.write('\nsource /etc/network/interfaces.d/*')